The present invention relates to transeptal access systems for accessing the left atrium from the right atrium by crossing the fossa ovalis. In particular, the present invention relates to devices and methods for locating the fossa ovalis.
The typical human heart includes a right ventricle, a right atrium, left ventricle and left atrium. The right atrium is in fluid communication with the superior vena cava and the inferior vena cava. The tricuspid valve separates the right atrium from the right ventricle. On the inner wall of the right atrium where it is separated from the left atrium is a thin walled, recessed portion, the fossa ovalis. In the heart of a fetus, the fossa ovalis is open (patent foramen), permitting fetal blood to flow between the right and left atria, bypassing the fetal lungs in favor of the placental blood flow. In most individuals, this opening closes after birth. In as many as about 5 percent of adults an opening (the patent foramen) still remains in place of the fossa ovalis between the right and left atria.
A wide variety of diagnostic and therapeutic procedures have been developed in which a catheter is transluminally advanced into various chambers and across valves of the heart. The most difficult chamber of the heart to access with a catheter is the left atrium. Access to the left atrium through the pulmonary artery is not possible. Approaches from the left ventricle are difficult, may cause arrhythmias and may present difficulty in obtaining stable catheter positioning. Accordingly, the presently preferred method of accessing the left atrium is through a transeptal approach, achieved by catheterization of the right atrium with subsequent penetration of the interatrial septum. The reduced wall thickness and location of the fossa ovalis makes it a useful access point for a transeptal access puncture.
A variety of risks are attendant to transeptal catheterization, in addition to the risks associated with normal heart catheterization. The primary additional risk is that associated with inaccurate identification and localization of the atrial septum and the fossa ovalis in particular. Improper placement of the catheter tip prior to the transeptal puncture presents the risk of puncture of tissue other than the interatrial septum, such as the aorta and the posterior wall of the right or left atrium. For this reason, catheterization is accompanied by fluoroscopy or other visualizing techniques to assist in properly locating the catheter tip in relation to the septum.
The objectives of left atrial access can be either diagnostic or therapeutic. One diagnostic use is pressure measurement in the left atrium. In the setting of an obstructed mitral valve (mitral stenosis), left atrial access allows a determination of the pressure difference between the left atrium and left ventricle. Left atrial access also allows entry into the left ventricle through the mitral valve. This is desirable when an artificial aortic valve is in place. The advent of aortic valve replacement with mechanical artificial valves, and the increase in the aged population and growing longevity of that population subsequent to aortic valve replacement, brings a greater need to evaluate the late stage functionality of such artificial valves.
Diagnostic measurement of the left ventricular pressures are, therefore, desirable to allow evaluation of mechanical artificial aortic valves post-replacement. It may be unsafe to cross these mechanical artificial valves retrograde from the aorta; therefore, access to the left ventricle by the antegrade route using a transeptal puncture is the preferred approach. Once a catheter has been placed in the left atrium using the transeptal approach, access to the left ventricle can be gained by advancing catheters across the mitral valve.
Many diagnostic indications exist for left atrial pressure measurements in addition to evaluating the functionality of artificial mitral valves. Other diagnostic indications for accessing the left ventricle via the antegrade transeptal approach include aortic stenosis, when a cardiologist is unable to pass a catheter retrograde into the left ventricle, and some disease states where the antegrade approach is considered preferable, such as subaortic obstruction.
Presently, the therapeutic objectives of left atrial access are primarily two-fold. The first is mitral valvuloplasty which represents an alternative to surgical procedures to relieve obstruction of the mitral valve. The second therapeutic objective is for electrophysiological intervention in the left atrium. Catheter ablation involves the placement of energy (typically RF) through a catheter, into various locations of the heart to eradicate inappropriate electrical pathways affecting the heart function. When these locations are in the left atrium, the catheter through which the radio frequency generator is placed typically is itself placed with transeptal catheterization. More recently, therapeutic treatment of the left atrial appendage to reduce the risk of embolic stroke has also been proposed.
Despite clinical acceptance of a wide variety of procedures which require access to the left atrium, significant room for improvement remains in the actual access technique. For example, the step of locating an appropriate site on the septum such as the fossa ovalis is highly technique dependant and can be inaccurate. This increases procedure time, and creates a risk that the needle will pierce the heart wall in an unnecessary and potentially undesirable location. Thus, there remains a need for a device and method for quickly and accurately locating and piercing the fossa ovalis to permit rapid and accurate transeptal access.
In accordance with one aspect of the present invention, there is provided a method of locating the fossa ovalis. The method comprises the steps of positioning the distal tip of a catheter in the heart, and propagating a signal from the catheter. A return signal is received by the catheter, and the tip of the catheter is moved to a position in which the return signal is indicative of the fossa ovalis.
In one embodiment, the propagating a signal step comprises propagating an ultrasound signal. Alternatively, the propagating a signal step comprises propagating an electromagnetic signal such as a signal in the UV-visible or IR range. Preferably, the electromagnetic signal comprises multiple wavelengths, including at least one of red, green and blue light.
In accordance with another aspect of the present invention, there is provided a trans septal access system. The system comprises a sheath, a dilator, a needle, and a signal transmitting surface and a signal receiving surface on at least one of the sheath, dilator and a needle, for transmitting a signal and receiving a return signal.
In one embodiment, the signal transmitting surface and the signal receiving surface comprise the same surface. The signal transmitting surface and/or the signal receiving surface may be the distal end of a waveguide. Alternatively, the signal transmitting surface and/or signal receiving surface may be a transducer. Preferably, the system further comprises a source of light, such as red, green and blue light, in communication with the signal transmitting surface. A detector capable of evaluating the frequency and intensity of the return signal is provided in communication with the signal receiving surface.
In accordance with a further aspect of the present invention, there is provided a method of locating the fossa ovalis. The method comprises the steps of bringing a catheter into contact with the surface of the septum between the right and left atria, and moving the catheter along the septum. Color absorption either within or beyond the septum is monitored for a change which is indicative of the location of the fossa ovalis. Preferably, the monitoring step comprises detecting reflected light. Thus, the method preferably comprises the step of transmitting light distally through the catheter to the septum, and receiving reflected light proximally through the catheter to a detector.